The Origin of Species

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Chapter 24.
The Origin of Species
Both in space and time, we seem to be brought
somewhat near to that great factthat mystery of
mysteriesthe first appearance of new beings on
this Earth. Darwin
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What is a species?

• Biological species concept
• defined by Ernst Mayr
• population whose members can interbreed produce
  viable, fertile offspring
• reproductively compatible

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Biological species concept
Western Meadowlark

• Eastern Meadowlark

Similar body colorations, but are distinct
biological species because their songs other
behaviors are different enough to prevent
interbreeding
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Diversity Taxonomy

• The Tree of Life
• species are the smallest unit at the ends of
  branches
• basic unit for organizing categorizing living
  things
• smallest unit by which we measure diversity

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How and why do new species originate?

• Reproductive isolation
• biological barriers that impede members from
  producing viable offspring
• before vs. after fertilization
• pre-zygotic barriers
• before the zygote (sperm vs egg)
• post-zygotic barriers
• after the zygote

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Pre-zygotic barriers

• Impede mating or hinder fertilization if mating
  occurs
• habitat isolation
• temporal isolation
• behavioral isolation
• mechanical isolation
• gametic isolation

male Frigate bird displaying to attract females
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Ecological isolation

• Two species may occupy different habitats within
  same area so may encounter each other rarely

2 species of garter snake, Thamnophis, occur in
same area, but one lives in water other is
terrestrial

• lions tigers could hybridize, but they live in
  different habitats
• lions in grasslands
• tigers in forest

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Temporal isolation

• Species that breed during different times of day,
  different seasons, or different years cannot mix
  gametes

Eastern spotted skunk (L) western spotted skunk
(R) overlap in range but eastern mates in late
winter western mates in late summer
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Behavioral isolation

• Courtship rituals that attract mates other
  unique behaviors to a species are effective
  reproductive barriers

Blue footed boobies mate only after a courtship
display unique to their species
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Gray-Crowned Cranes engaged in courtship display,
Kenya
What can you say?
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End of Part 1

• Go to Part 2 of The Origin of Species